Following single injections of the same dose of protein-rich extracts (E-RNA) from either virulent SR-11 or attenuated RIA strains of Salmonella typhimurium, significant protection against 100 or 1000 LD50 doses of virulent salmonellae with concomitant manifestations of immunogen-specific cell-mediated immunity can be readily induced in ICR Swiss mice but not in highly susceptible C57B1/6f mice. In contrast to the C57B1/6f mouse, the outbred Swiss mouse is capable of forming a significant antigen-specific T cell (sensitive to anti-theta serum) response in its lymph nodes. To determine whether T lymphocyte responses are responsible for microbicidal activity against virulent salmonellae exhibited by immune lymphoid cultures (peritoneal, spleen and lymph node cells), the efficacy of cytotoxic anti-theta serum to abrogate this microbicidal capacity will be assayed. Repeated injections of C57B1/6f mice with the E-RNA extracts or S. typhimurium RIA will be done to determine whether an effective resistance to lethal salmonellosis may be achieved. Further attempts to separate chromatographically the proteins in the immunogenic extracts are to be continued as is an analysis of immunologically "identical" soluble protein complexes present in defined culture medium in which either S. typhimurium strain is grown. A dissociation of the IgM antibody response from the cell-mediated responses has been accomplished in Swiss mice immunized with polymerized E-RNA extracts; mice so immunized exhibit markedly diminished cell- mediated immune responses and significantly greater lethality to virulent S. typhimurium than do mice immunized with unpolymerized E-RNA extracts. This antigen-specific IgM will be examined for its cytophilic potential since cytophilic IgM directed against the proteins of E-RNA is the only antibody response detectable in Swiss mice immunized with unpolymerized E-RNA extracts.